The present invention relates generally to a differential gear assembly and more particularly to a differential gear assembly utilizing an Eddy-current retarder to limit relative rotation of gears.
Differential gear assemblies are utilized to translate drive shaft rotation into left and right axle shaft rotation, which in turn provides vehicle drive at the wheels. Conventional vehicle differential assemblies allow the wheels to rotate at different rates. This is necessary during vehicle turning when the outside wheel will rotate faster than the inside wheel. This is commonly accomplished through the use of differential side gears and pinion gears located inside the differential case. The differential side gears, each splined to an axle shaft, will rotate relative to the differential case and relative to each other. This process is called differentiation, and allows the vehicle to be turned without dragging the tires along the road.
One form of differential assembly is commonly known as xe2x80x9copenxe2x80x9d differential. An xe2x80x9copenxe2x80x9d differential is a differential assembly without a torque biasing mechanism. In such a system, when the vehicle is driving straight, and a difference in road friction, or traction, exists between the right and left tires, the rotational motion of the differential is transmitted mostly to the wheel with the least grip/lower friction. It is further known that in such xe2x80x9copenxe2x80x9d differentials, the maximum torque delivered to both wheels is twice the torque delivered to the wheel with less traction. This means, that if one tire is placed on a low friction surface, it receives almost zero driveline torque. In addition, the other tire also receives almost zero torque, regardless of the traction available at that tire. To further exacerbate these characteristics, if the torque delivered to the wheel with the less traction exceeds the friction torque acting on the tire-road interface, the wheel slips. Since the coefficient of dynamic/sliding friction is commonly less than the static/non-sliding friction, a slipping wheel has even less traction than when it is not slipping. Thus, the torque delivered to both wheels is further reduced.
It is known that if the relative motion between the two side gears can be stopped or limited, than both wheels would be forced to rotate at the same speed as the differential, regardless of any difference in traction between the differentiated wheels. By reducing the relative motion, differentiation can be essentially stopped. Unequal amounts of torque can be sent to each wheel, proportional to the difference in traction between the two wheels. This allows the torque to be delivered where it can best be utilized. The mechanism which applies more torque to the wheel with higher traction, yet still allows differentiation, is called a torque-biasing differential.
Known torque biasing differentials often rely on a friction interface between one of the differential gears (side gear, pinion gear, or reasonable facsimile) in the differential case (the differential gear container which is attached to the ring/driven gear and receives torque from the pinion/driving gear). Although this configuration creates a torque biasing differential, it commonly has several known disadvantages. One disadvantage stems from the fact that this configuration provides passive torque bias. With passive torque bias, the bias is fixed during operation and cannot be modified or adjusted to accommodate for performance or driving conditions. A second disadvantage stems from the fact this configuration will often wear during operation. It is known that the wear (or loss of material) during operation can negatively affect or degrade the torque bias provided by this configuration. A third disadvantage of this known configuration can arise from harsh engagement or shudder (a stick/slip phenomenon) during operation. It is possible for these engagement issues to provide unacceptable NVH issues that can result in decreased customer satisfaction.
It would, therefore, be highly desirable to have an assembly for providing torque bias that could provide an active control and would reduce the wear associated with known friction interface configurations. It would additionally be highly desirable to have an assembly for providing torque bias that could reduce the engagement/NVH issues associated with friction interface designs.
It is, therefore, an object of the present invention to provide a differential assembly with active torque bias control. It is a further object of the present invention to provide a differential assembly with reduced wear and reduced engagement/NVH issues.
In accordance with the objects of the present invention, a differential assembly is provided. The differential assembly includes a first differential side gear and a second differential side gear. An Eddy-current retarder, positioned in communication with the first differential side gear and the second differential side gear, is utilized to create torque bias between the first differential side gear and the second differential side gear.
Other objects and features of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.